file upload issue on server

Hi all,
Please help me,
i have issue on server, my application have file upload control it work fine on local machine but on server its not work proper. in my application have functionality like, user upload all types of file from file upload control and user can replace the file. when user want's to replace file then in my application asked to user for "replace the existing file with new file" if user says "Yes". In application existing file will delete and new file will copy. it also work on server but issue comes when first uploaded file size is small and replacing file size is big then its not work.

Thanks in advance,

protected void btnUpload_Click(object sender, EventArgs e)
       {
           Button btn = (Button)sender;
           int Flag = 0;
           string FileName = createNameForFile(btn.CommandArgument);//Returns Created File Name For the Question.
           Session["QuestionId"] = btn.CommandArgument;
           for (int i = 0; i < dtlViewDetails.Controls.Count; i++)
           {
               DataList DataList2 = (DataList)dtlViewDetails.Controls[i].FindControl("DataList2");
               for (int j = 0; j < DataList2.Controls.Count; j++)
               {
                   Label QuestionId = (Label)DataList2.Controls[j].FindControl("lblQuestionId");

                   Label lblHiddenFileName = (Label)DataList2.Controls[j].FindControl("lblHiddenFileName");
                   FileUpload Uploader = (FileUpload)DataList2.Controls[j].FindControl("fuAttachment");
                   LinkButton lnkView = (LinkButton)DataList2.Controls[j].FindControl("lnkView");
                   TextBox txtAnswerTypeDesc = (TextBox)DataList2.Controls[j].FindControl("txtAnswerTypeDesc");
                   Label lblerrorMessageHtmlCell = (Label)DataList2.Controls[j].FindControl("lblerrorMessageHtmlCell");
                   TextBox txtAttachFileDesc = (TextBox)DataList2.Controls[j].FindControl("txtAttachFileDesc");

                   if (lblHiddenFileName.Text == "")
                   {
                       if (Convert.ToInt32(QuestionId.Text) == Convert.ToInt32(btn.CommandArgument))
                       {
                           if (Uploader.HasFile)
                           {
                               lblerrorMessageHtmlCell.Visible = false;
                               FileInfo filedet = new FileInfo(Uploader.FileName);
                               string FileNameToCheck = Server.MapPath(DocumentPath + FileName) + filedet.Extension;
                               Uploader.SaveAs(Server.MapPath(DocumentPath + Uploader.FileName));
                               string OriginalName = Server.MapPath(DocumentPath + Uploader.FileName);
                               File.Copy(OriginalName, FileNameToCheck);
                               File.Delete(OriginalName);
                               lblHiddenFileName.Text = FileName + filedet.Extension;
                               lnkView.Visible = true;
                               Flag = 1;
                               break;
                           }
                           else
                           {
                               lblerrorMessageHtmlCell.Visible = true;
                               lblerrorMessageHtmlCell.Text = "No File To Upload.";
                               lblerrorMessageHtmlCell.ForeColor = System.Drawing.Color.Red;
                               Flag = 1;
                               break;
                           }
                       }
                   }
                   else
                   {
                       if (Uploader.HasFile)
                       {
                           lblerrorMessageHtmlCell.Visible = false;
                           Session["FileUploadObject"] = Uploader;
                           Session["FileNameToCheck"] = FileName;
                           Session["LabelFileName"] = lblHiddenFileName.Text;
                           trQuestionaries.Visible = false;
                           trPopupYesNo.Visible = true;
                           //Console.Beep(600, 300);
                       }
                       else
                       {
                           if (Convert.ToInt32(QuestionId.Text) == Convert.ToInt32(btn.CommandArgument))
                           {
                               lblerrorMessageHtmlCell.Visible = true;
                               lblerrorMessageHtmlCell.Text = "No File To Upload.";
                               lblerrorMessag

Tags: C#, ASP.NET